Serum antibody response to oral infection precedes but does not prevent Porphyromonas gingivalis-induced alveolar bone loss in mice

Maintaining homeostatic control of periodontal bone tissue

Alveolar bone is a unique osseous tissue due to the proximity of dental plaque biofilms. Periodontal health and homeostasis are mediated by a balanced host immune response to these polymicrobial biofilms. Dysbiotic shifts within dental plaque biofilms can drive a proinflammatory immune response state in the periodontal epithelial and gingival connective tissues, which leads to paracrine signaling to subjacent bone cells. Sustained chronic periodontal inflammation disrupts "coupled" osteoclast-osteoblast actions, which ultimately result in alveolar bone destruction. This chapter will provide an overview of alveolar bone physiology and will highlight why the oral microbiota is a critical regulator of alveolar bone remodeling. The ecology of dental plaque biofilms will be discussed in the context that periodontitis is a polymicrobial disruption of host homeostasis. The pathogenesis of periodontal bone loss will be explained from both a historical and current perspective, providing the opportunity to revisit the role of fibrosis in alveolar bone destruction. Periodontal immune cell interactions with bone cells will be reviewed based on our current understanding of osteoimmunological mechanisms influencing alveolar bone remodeling. Lastly, probiotic and prebiotic interventions in the oral microbiota will be evaluated as potential noninvasive therapies to support alveolar bone homeostasis and prevent periodontal bone loss.

Polymicrobial synergy within oral biofilm promotes invasion of dendritic cells and survival of consortia members

Years of human microbiome research have confirmed that microbes rarely live or function alone, favoring diverse communities. Yet most experimental host-pathogen studies employ single species models of infection. Here, the influence of three-species oral microbial consortium on growth, virulence, invasion and persistence in dendritic cells (DCs) was examined experimentally in human monocyte-derived dendritic cells (DCs) and in patients with periodontitis (PD). Cooperative biofilm formation by Streptococcus gordonii, Fusobacterium nucleatum and Porphyromonas gingivalis was documented in vitro using growth models and scanning electron microscopy. Analysis of growth rates by species-specific 16s rRNA probes revealed distinct, early advantages to consortium growth for S. gordonii and F. nucleatum with P. gingivalis, while P. gingivalis upregulated its short mfa1 fimbriae, leading to increased invasion of DCs. F. nucleatum was only taken up by DCs when in consortium with P. gingivalis. Mature consortium regressed DC maturation upon uptake, as determined by flow cytometry. Analysis of dental plaques of PD and healthy subjects by 16s rRNA confirmed oral colonization with consortium members, but DC hematogenous spread was limited to P. gingivalis and F. nucleatum. Expression of P. gingivalis mfa1 fimbriae was increased in dental plaques and hematogenous DCs of PD patients. P. gingivalis in the consortium correlated with an adverse clinical response in the gingiva of PD subjects. In conclusion, we have identified polymicrobial synergy in a three-species oral consortium that may have negative consequences for the host, including microbial dissemination and adverse peripheral inflammatory responses.

Potassium Channel-blockers as Therapeutic Agents to Interfere with Bone Resorption of Periodontal Disease

Inflammatory lesions of periodontal disease contain all the cellular components, including abundant activated/memory T- and B-cells, necessary to control immunological interactive networks and to accelerate bone resorption by RANKL-dependent and -independent mechanisms. Blockade of RANKL function has been shown to ameliorate periodontal bone resorption and other osteopenic disorders without affecting inflammation. Development of therapies aimed at decreasing the expression of RANKL and pro-inflammatory cytokines by T-cells constitutes a promising strategy to ameliorate not only bone resorption, but also inflammation. Several reports have demonstrated that the potassium channels Kv1.3 and IKCa1, through the use of selective blockers, play important roles in T-cell-mediated events, including T-cell proliferation and the production of pro-inflammatory cytokines. More recently, a potassium channel-blocker for Kv1.3 has been shown to down-regulate bone resorption by decreasing the ratio of RANKL-to-OPG expression by memory-activated T-cells. In this article, we first summarize the mechanisms by which chronically activated/memory T-cells, in concert with B-cells and macrophages, trigger inflammatory bone resorption. Then, we describe the main structural and functional characteristics of potassium channels Kv1.3 and IKCa1 in some of the cells implicated in periodontal disease progression. Finally, this review elucidates some recent advances in the use of potassium channel-blockers of Kv1.3 and IKCa1 to ameliorate the clinical signs or side-effects of several immunological disorders and to decrease inflammatory bone resorption in periodontal disease. ABBREVIATIONS: AICD, activation-induced cell death; APC, antigen-presenting cells; B(K), large conductance; CRAC, calcium release-activated calcium channels; DC, dendritic cell; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; IFN-γ, interferon-γ; IP3, inositol (1,4,5)-triphosphate; (K)ir, inward rectifier; JNK, c-Jun N-terminal kinase; I(K), intermediate conductance; LPS, lipopolysaccharide; L, ligand; MCSF, macrophage colony-stimulating factor; MHC, major histocompatibility complex; NFAT, nuclear factor of activated T-cells; RANK, receptor activator of nuclear factor-κB; TCM, central memory T-cells; TEM, effector memory T-cells; TNF, tumor necrosis factor; TRAIL, TNF-related apoptosis-inducing ligand; OPG, osteoprotegerin; Omp29, 29-kDa outer membrane protein; PKC, protein kinase C; PLC, phospholipase C; RT-PCR, reverse-transcriptase polymerase chain-reaction; S(K), small conductance; TCR, T-cell receptor; and (K)v, voltage-gated.

Humoral immune responses to periodontal pathogens in the elderly

PURPOSE

Elderly people are thought to be more susceptible to periodontal disease due to reduced immune function associated with aging. However, little information is available on the nature of immune responses against putative periodontal pathogens in geriatric patients. The purpose of this study was to evaluate the serum IgG antibody responses to six periodontal pathogens in geriatric subjects.

METHODS

The study population consisted of 85 geriatric patients and was divided into three groups: 29 mild (MCP), 27 moderate (MoCP) and 29 severe (SCP) chronic periodontitis patients. Serum levels of IgG antibody to Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum and Prevotella intermedia were measured by enzyme-linked immunosorbent assay (ELISA) and compared among the groups.

RESULTS

All three groups showed levels of serum IgG in response to P. gingivalis, A. actinomycetemcomitans, and P. intermedia that were three to four times higher than levels of IgG to T. forsythia, T. denticola, and F. nucleatum. There were no significant differences among all three groups in IgG response to P. gingivalis (P=0.065), T. forsythia (P=0.057), T. denticola (P=0.1), and P. intermedia (P=0.167), although the IgG levels tended to be higher in patients with SCP than in those with MCP or MoCP (with the exception of those for P. intermedia). In contrast, there were significant differences among the groups in IgG levels in response to F. nucleatum (P=0.001) and A. actinomycetemcomitans (P=0.003). IgG levels to A. actinomycetemcomitans were higher in patients with MCP than in those with MoCP or SCP.

CONCLUSIONS

When IgG levels were compared among three periodontal disease groups, only IgG levels to F. nucleatum significantly increased with the severity of disease. On the contrary, IgG levels to A. actinomycetemcomitans decreased significantly in patients with SCP compared to those with MCP. There were no significant differences in the IgG levels for P. gingivalis, T. forsythia, T. denticola, and P. intermedia among geriatric patients with chronic periodontitis.

The inflammophilic character of the periodontitis-associated microbiota

In periodontitis, dysbiotic microbial communities exhibit synergistic interactions for enhanced protection from host defenses, nutrient acquisition, and persistence in an inflammatory environment. This review discusses evidence that periodontitis-associated communities are 'inflammo-philic' (=loving or attracted to inflammation) in that they have evolved to not only endure inflammation but also to take advantage of it. In this regard, inflammation can drive the selection and enrichment of these pathogenic communities by providing a source of nutrients in the form of tissue breakdown products (e.g. degraded collagen peptides and heme-containing compounds). In contrast, those species that cannot benefit from the altered ecological conditions of the inflammatory environment, or for which host inflammation is detrimental, are likely to be outcompeted. Consistent with the concept that inflammation fosters the growth of dysbiotic microbial communities, the bacterial biomass of human periodontitis-associated biofilms was shown to increase with increasing periodontal inflammation. Conversely, anti-inflammatory treatments in animal models of periodontitis were shown to diminish the periodontal bacterial load, in addition to protecting from bone loss. The selective flourishing of inflammophilic bacteria can perpetuate inflammatory tissue destruction by setting off a 'vicious cycle' for disease progression, in which dysbiosis and inflammation reinforce each other. Therefore, the control of inflammation appears to be central to the treatment of periodontitis, as it is likely to control both dysbiosis and disease progression.

A mouse model for pathogen-induced chronic inflammation at local and systemic sites

Chronic inflammation is a major driver of pathological tissue damage and a unifying characteristic of many chronic diseases in humans including neoplastic, autoimmune, and chronic inflammatory diseases. Emerging evidence implicates pathogen-induced chronic inflammation in the development and progression of chronic diseases with a wide variety of clinical manifestations. Due to the complex and multifactorial etiology of chronic disease, designing experiments for proof of causality and the establishment of mechanistic links is nearly impossible in humans. An advantage of using animal models is that both genetic and environmental factors that may influence the course of a particular disease can be controlled. Thus, designing relevant animal models of infection represents a key step in identifying host and pathogen specific mechanisms that contribute to chronic inflammation. Here we describe a mouse model of pathogen-induced chronic inflammation at local and systemic sites following infection with the oral pathogen Porphyromonas gingivalis, a bacterium closely associated with human periodontal disease. Oral infection of specific-pathogen free mice induces a local inflammatory response resulting in destruction of tooth supporting alveolar bone, a hallmark of periodontal disease. In an established mouse model of atherosclerosis, infection with P. gingivalis accelerates inflammatory plaque deposition within the aortic sinus and innominate artery, accompanied by activation of the vascular endothelium, an increased immune cell infiltrate, and elevated expression of inflammatory mediators within lesions. We detail methodologies for the assessment of inflammation at local and systemic sites. The use of transgenic mice and defined bacterial mutants makes this model particularly suitable for identifying both host and microbial factors involved in the initiation, progression, and outcome of disease. Additionally, the model can be used to screen for novel therapeutic strategies, including vaccination and pharmacological intervention.

Experimental periodontitis induced by Porphyromonas gingivalis does not alter the onset or severity of diabetes in mice

BACKGROUND AND OBJECTIVE

Diabetes mellitus is believed to increase the risk and severity of periodontitis. However, less evidence is available on the converse effects of periodontitis on diabetes. The objective of the study was to investigate to what degree experimental periodontitis induced by Porphyromonas gingivalis might influence the onset and severity of diabetes in different mouse models.

MATERIAL AND METHODS

Twenty-eight male Tallyho/JngJ mice (type 2 diabetes), 20 male streptozotocin-induced diabetes C57BL/6J mice (type 1 diabetes) and 20 male C57BL/6J mice at 4 wks of age were evenly divided into two groups: periodontal infection and sham infection. Periodontitis was induced by Porphyromonas gingivalis W50 (P. gingivalis) oral inoculation before the development of diabetes. Sham-infected mice received vehicle as control. P. gingivalis in the oral cavity were identified by quantitative polymerase chain reaction. Fasting glucose, body weight and food intake levels were monitored and glucose tolerance tests were performed to assess glucose homeostasis for the onset and progression of diabetes. The level of alveolar bone loss and tumor necrosis factor-alpha were determined in week 20 when mice were killed.

RESULTS

Mice in the infection groups developed more alveolar bone loss than those in sham-infection groups (Tallyho p = 0.021; C57-STZ p = 0.014; C57 p = 0.035). Hyperglycemic mice exhibited significantly more bone loss compared to those normal glucose mice (Tallyho vs. C57 p = 0.029; C57-STZ vs. C57 p = 0.024). The level of tumor necrosis factor-alpha was consistent with that of periodontal bone loss and hyperglycemia. There was no significant effect of mouse species on the amount of bone loss at the same level of blood glucose. No statistically significant difference or trend in glucose metabolism was found between the infection and sham-infection group.

CONCLUSION

Diabetes enhanced the risk for periodontal disease induced by P. gingivalis. However, no converse impact was found between this periodontal infection and onset and severity of diabetes in both type 1 and 2 diabetes mice.

The formation of immune complexes is involved in the acute phase of periodontal destruction in rats

BACKGROUND AND OBJECTIVE

Loss of clinical attachment and alveolar bone destruction are major symptoms of periodontitis, caused by not only the destructive effect of periodontopathic bacteria but also the overactive response of the host immune system against periodontal pathogens. The details of the participation of the immune system in the onset and progression of periodontitis are unclear. In this study, we attempted to determine whether the host immune system, and in particular the formation of immune complexes, is involved in the periodontal destruction.

MATERIAL AND METHODS

We applied ovalbumin or lipopolysaccharide (LPS) as antigens and their specific immunoglobulin G (IgG) antibodies purified from rat serum to rat gingival sulcus alternately. Loss of attachment, alveolar bone destruction and the numbers of inflammatory cells infiltrating the periodontal tissue and osteoclasts on the alveolar bone surface were investigated histometrically. The formation of immune complex was confirmed by immunohistological staining of complement C1qB.

RESULTS

Loss of attachment and the presence of C1qB were observed histopathologically in both experimental groups. The group that had been treated with LPS and anti-LPS IgG showed greater loss of attachment. The number of inflammatory cells in the periodontal tissue was increased in both experimental groups, while osteoclasts at the alveolar bone crest were observed only in the group that had been treated with LPS and anti-LPS IgG.

CONCLUSION

In the present study, we showed that the formation of immune complex appears to be involved in the acute phase of periodontal destruction and that the biological activity of antigens is also important.

Virulence of major periodontal pathogens and lack of humoral immune protection in a rat model of periodontal disease

OBJECTIVE

This study was designed to test the hypothesis that periodontal pathogens Tannerella forsythia and Porphyromonas gingivalis are synergistic in terms of virulence potential using a model of mixed-microbial infection in rats.

MATERIALS AND METHODS

Three groups of rats were infected orally with either T. forsythia or P. gingivalis in mono-bacterial infections or as mixed-microbial infections for 12 weeks and a sham-infected group were used as a control. This study examined bacterial infection, inflammation, immunity, and alveolar bone loss changes with disease progression.

RESULTS

Tannerella forsythia and P. gingivalis genomic DNA was detected in microbial samples from infected rats by PCR indicating their colonization in the rat oral cavity. Primary infection induced significantly high IgG, IgG2b, IgG1, and IgG2a antibody levels indicating activation of mixed Th1 and Th2 immune responses. Rats infected with the mixed-microbial consortium exhibited significantly increased palatal horizontal and interproximal alveolar bone loss. Histological examinations indicated significant hyperplasia of the gingival epithelium with moderate inflammatory infiltration and apical migration of junctional epithelium. The results observed differ compared to uninfected controls.

CONCLUSION

Our results indicated that T. forsythia and P. gingivalis exhibit virulence, but not virulence synergy, resulting in the immuno-inflammatory responses and lack of humoral immune protection during periodontitis in rats.

Role of Porphyromonas gingivalis phosphoserine phosphatase enzyme SerB in inflammation, immune response, and induction of alveolar bone resorption in rats

Porphyromonas gingivalis secretes a serine phosphatase enzyme, SerB, upon contact with gingival epithelial cells in vitro. The SerB protein plays a critical role in internalization and survival of the organism in epithelial cells. SerB is also responsible for the inhibition of interleukin-8 (IL-8) secretion from gingival epithelial cells infected with P. gingivalis. This study examined the ability of a P. gingivalis SerB mutant to colonize the oral cavity and induce gingival inflammation, immune responses, and alveolar bone resorption in a rat model of periodontal disease. Both P. gingivalis ATCC 33277 and an isogenic ΔSerB mutant colonized the oral cavities of rats during the 12-week experimental period. Both of the strains induced significant (P < 0.05) systemic levels of immunoglobulin G (IgG) and isotypes IgG1, IgG2a, and IgG2b, indicating the involvement of both T helper type 1 (Th1) and Th2 responses to infection. Both strains induced significantly (P < 0.05) higher levels of alveolar bone resorption in infected rats than in sham-infected control rats. However, horizontal and interproximal alveolar bone resorption induced by the SerB mutant was significantly (P < 0.05) lower than that induced by the parental strain. Rats infected with the ΔSerB mutant exhibited significantly higher levels of apical migration of the junctional epithelium (P < 0.01) and polymorphonuclear neutrophil (PMN) recruitment (P < 0.001) into the gingival tissues than rats infected with the wild type. In conclusion, in a rat model of periodontal disease, the SerB phosphatase of P. gingivalis is required for maximal alveolar bone resorption, and in the absence of SerB, more PMNs are recruited into the gingival tissues.

Porphyromonas gingivalis and Treponema denticola Mixed Microbial Infection in a Rat Model of Periodontal Disease

Porphyromonas gingivalis and Treponema denticola are periodontal pathogens that express virulence factors associated with the pathogenesis of periodontitis. In this paper we tested the hypothesis that P. gingivalis and T. denticola are synergistic in terms of virulence; using a model of mixed microbial infection in rats. Groups of rats were orally infected with either P. gingivalis or T. denticola or mixed microbial infections for 7 and 12 weeks. P. gingivalis genomic DNA was detected more frequently by PCR than T. denticola. Both bacteria induced significantly high IgG, IgG2b, IgG1, IgG2a antibody levels indicating a stimulation of Th1 and Th2 immune response. Radiographic and morphometric measurements demonstrated that rats infected with the mixed infection exhibited significantly more alveolar bone loss than shaminfected control rats. Histology revealed apical migration of junctional epithelium, rete ridge elongation, and crestal alveolar bone resorption; resembling periodontal disease lesion. These results showed that P. gingivalis and T. denticola exhibit no synergistic virulence in a rat model of periodontal disease.

B Cell IgD Deletion Prevents Alveolar Bone Loss Following Murine Oral Infection

Periodontal disease is one of the most common infectious diseases of humans. Immune responses to infection trigger loss of alveolar bone from the jaw and eventual tooth loss. We investigated the contribution of B cell IgD to alveolar bone loss by comparing the response of B cell normal BALB/cJ mice and IgD deficient BALB/c-Igh-5^−/−J mice to oral infection with Porphyromonas gingivalis, a gram-negative periodontopathic bacterium from humans. P. gingivalis-infected normal mice lost bone. Specific antibody to P. gingivalis was lower and oral colonization was higher in IgD deficient mice; yet bone loss was completely absent. Infection increased the proportion of CD69⁺ activated B cells and CD4⁺ T cells in immune normal mice compared to IgD deficient mice. These data suggest that IgD is an important mediator of alveolar bone resorption, possibly through antigen-specific coactivation of B cells and CD4⁺ T cells.

An essential role for IL-17 in preventing pathogen-initiated bone destruction: recruitment of neutrophils to inflamed bone requires IL-17 receptor-dependent signals

IL-17 and its receptor are founding members of a novel family of inflammatory cytokines. IL-17 plays a pathogenic role in rheumatoid arthritis (RA)-associated bone destruction. However, IL-17 is also an important regulator of host defense through granulopoiesis and neutrophil trafficking. Therefore, the role of IL-17 in pathogen-initiated bone loss was not obvious. The most common form of infection-induced bone destruction occurs in periodontal disease (PD). In addition to causing significant morbidity, PD is a risk factor for atherosclerotic heart disease and chronic obstructive pulmonary disease (COPD). Similar to RA, bone destruction in PD is caused by the immune response. However, neutrophils provide critical antimicrobial defense against periodontal organisms. Since IL-17 is bone destructive in RA but a key regulator of neutrophils, we examined its role in inflammatory bone loss induced by the oral pathogen Porphyromonas gingivalis in IL-17RA-deficient mice. These mice showed enhanced periodontal bone destruction, suggesting a bone-protective role for IL-17, reminiscent of a neutrophil deficiency. Although IL-17RA-deficient neutrophils functioned normally ex vivo, IL-17RA knock-out (IL-17RA(KO)) mice exhibited reduced serum chemokine levels and concomitantly reduced neutrophil migration to bone. Consistently, CXCR2(KO) mice were highly susceptible to alveolar bone loss; interestingly, these mice also suggested a role for chemokines in maintaining normal bone homeostasis. These results indicate a nonredundant role for IL-17 in mediating host defense via neutrophil mobilization.

Protective and destructive immunity in the periodontium: Part 1--innate and humoral immunity and the periodontium

Based on the results of recent research in the field, the present paper will discuss the protective and destructive aspects of the innate vs. adaptive (humoral and cell-mediated) immunity associated with the bacterial virulent factors or antigenic determinants during periodontal pathogenesis. Attention will be focused on: (i) the Toll-like receptors (TLR), the innate immune repertoire for recognizing the unique molecular patterns of microbial components that trigger innate and adaptive immunity for effective host defenses, in some general non-oral vs. periodontal microbial infections; (ii) T-cell-mediated immunity, Th-cytokines, and osteoclastogenesis in periodontal disease progression; and (iii) some molecular techniques developed and used to identify critical microbial virulence factors or antigens associated with host immunity (using Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis as the model species). Therefore, further understanding of the molecular interactions and mechanisms associated with the host's innate and adaptive immune responses will facilitate the development of new and innovative therapeutics for future periodontal treatments.

T-cell expression cloning of Porphyromonas gingivalis genes coding for T helper-biased immune responses during infection

Exposure of the mouse oral cavity to Porphyromonas gingivalis results in the development of gingivitis and periapical bone loss, which apparently are associated with a Th1 response to bacterial antigens. We have used this infection model in conjunction with direct T-cell expression cloning to identify bacterial antigens that induce a preferential or biased T helper response during the infectious process. A P. gingivalis-specific CD4 T-cell line derived from mice at 3 weeks postchallenge was used to directly screen a P. gingivalis genomic expression library. This screen resulted in the identification of five genes coding for previously identified proteins and three other putative protein antigens. One of the identified proteins, P. gingivalis thiol peroxidase, was studied in detail because this molecule belongs to a protein family that is apparently involved in microbial pathogenesis. Infection of mice with P. gingivalis, either via the subcutaneous route or after exposure of the animal's oral cavity to viable bacteria, resulted in the induction of a strong thiol peroxidase-specific immune response characterized by the production of high titers of specific serum immunoglobulin G2a antibody and the production of gamma interferon by antigen-stimulated lymphoid cells, a typical Th1-biased response. Thus, the use of a proven T-cell expression cloning approach and a mouse model of periodontal disease resulted in the identification and characterization of P. gingivalis proteins that might be involved in pathogenesis.

Three-dimensional quantification of alveolar bone loss in Porphyromonas gingivalis-infected mice using micro-computed tomography

BACKGROUND

Animal models are routinely used for the study of the pathogenesis of periodontal disease. However, some of the methods used for evaluating alveolar bone loss are limited to linear or two dimension measurements, while other methods, such as histology, are labor consuming. The present study was designed to evaluate a novel method for assessing the volume of alveolar bone loss in mice and to compare it to the traditional morphometric (linear) technique.

METHODS

Seven- to 8-week-old BALB/c mice were divided into three equal groups of six each; two groups were infected orally with Porphyromonas gingivalis (P. gingivalis) 381 or 53,977, while the third group was used as non-infected control. Forty-two days following infection, serum samples were obtained and maxillae were harvested. Bone loss was evaluated by micro-computed tomography (micro-CT) and by the morphometric technique.

RESULTS

Significant decrease in residual supportive bone volumes (RSBV) was observed in both P. gingivalis-infected groups compared to the control group (P<0.0001). The P. gingivalis 53,977-infected group showed less residual supportive bone volume compared to the P. gingivalis 381-infected group, but there were no significant differences between these two groups. Using the morphometric technique, the differences between the three groups were not found to be statistically significant (P>0.05).

CONCLUSIONS

The present study describes a novel micro-CT technique for volumetric evaluation of alveolar bone loss in mice. This technique is relatively simple and accurate, and due to its high sensitivity, enables the investigator to reduce the number of animals needed in each experimental group.

Aging changes in the periodontal bone of F344/N rat

The aim of this research was to determine whether a rat was an adequate laboratory animal model for periodontal research on elderly humans. Thirty-two F344/NSlc female rats ranged between 30 and 1000 days of age were used. The alveolar bone loss around the molars was assessed by a morphometric method. A significant correlation was found between age and the amount of alveolar bone loss. For further analysis, the rats were grouped into four by age; 30-60 days, 220-430 days, 640-850 days, and more than 850 days. The means of alveolar bone loss were compared between age groups. It was found that the resorption of the alveolar bone around the molars of the rats continued until they were 1000-days-old, and this trend was stronger in the mandible than the maxilla. It was suggested that rats could be used as adequate laboratory animals for periodontal research.

The role of acquired immunity and periodontal disease progression

Our understanding of the pathogenesis in human periodontal diseases is limited by the lack of specific and sensitive tools or models to study the complex microbial challenges and their interactions with the host's immune system. Recent advances in cellular and molecular biology research have demonstrated the importance of the acquired immune system not only in fighting the virulent periodontal pathogens but also in protecting the host from developing further devastating conditions in periodontal infections. The use of genetic knockout and immunodeficient mouse strains has shown that the acquired immune response-in particular, CD4+ T-cells-plays a pivotal role in controlling the ongoing infection, the immune/inflammatory responses, and the subsequent host's tissue destruction. In particular, studies of the pathogen-specific CD4+ T-cell-mediated immunity have clarified the roles of: (i) the relative diverse immune repertoire involved in periodontal pathogenesis, (ii) the contribution of pathogen-associated Th1-Th2 cytokine expressions in periodontal disease progression, and (iii) micro-organism-triggered periodontal CD4+ T-cell-mediated osteoclastogenic factor, 'RANK-L', which is linked to the induction of alveolar bone destruction in situ. The present review will focus on some recent advances in the acquired immune responses involving B-cells, CD8+ T-cells, and CD4+ T-cells in the context of periodontal disease progression. New approaches will further facilitate our understanding of their underlying molecular mechanisms that may lead to the development of new treatment modalities for periodontal diseases and their associated complications.

Inhibitory effects of incadronate on the progression of rat experimental periodontitis by porphyromonas gingivalis infection

BACKGROUND

Incadronate (YM175, disodium cycloheptylaminomethylenediphosphonate monohydrate), a bisphosphonate, has been suggested to prevent the bone resorption associated with periodontitis by inhibiting osteoclast activity. The purpose of this study was to investigate the effect of incadronate in preventing periodontal destruction in rats with Porphyromonas gingivalis-induced periodontitis.

METHODS

Periodontitis was induced in 35 Wister rats by inoculating P. gingivalis into the oral cavity and feeding the rats a soft diet for 4 weeks. Incadronate or placebo was administered to the oral cavity of the rats 2 days per week for 2, 4, or 8 weeks.

RESULTS

P. gingivalis infection resulted in destruction of the periodontal ligament, reduced bone density, and caused inflammatory cell migration. Radiographic, morphometric, and histological results showed that incadronate had the ability to increase the bone mineral density (quantum level score; cortex 518.9 [placebo 612.8]; sponge 579.8 [placebo 672.0]) and to prevent periodontal ligament destruction (width 0.16 mm [placebo 0.20 mm]; area 0.36 mm2 [placebo 0.54 mm2]) after 8 weeks' administration. Furthermore, the polymorphonuclear leukocyte (PMN) infiltration in gingival tissue was significantly decreased.

CONCLUSION

These results showed that incadronate inhibits bone resorption and PMN migration in P. gingivalis-induced periodontitis.

Fusobacterium nucleatum impairs serum binding to Porphyromonas gingivalis biofilm

Mouse immune sera obtained by immunization with Fusobacterium nucleatum and then Porphyromonas gingivalis demonstrated an impaired binding capacity to P. gingivalis-biofilm and lower avidity to P. gingivalis when compared with sera obtained from mice immunized with P. gingivalis alone.

Prior exposure of mice to Fusobacterium nucleatum modulates host response to Porphyromonas gingivalis

Multiple periodontal pathogens sequentially colonize the subgingival niche during the conversion from gingivitis to destructive periodontal disease. An animal model of sequential immunization with key periodontal pathogens has been developed to determine whether T- and B-lymphocyte effector functions are skewed and fail to protect the host from pathogenic challenge. The present study was performed to evaluate the immunomodulatory effect of exposure to Fusobacterium nucleatum prior to Porphyromonas gingivalis. Group 1 (control) mice were immunized with phosphate-buffered saline, group 2 were immunized with F. nucleatum prior to P. gingivalis and group 3 were immunized with P. gingivalis alone. All the T-cell clones derived from group 2 demonstrated type 2 helper T-cell clone (Th2 subsets), whereas those from group 3 mice demonstrated Th1 subsets. Exposure of mice to F. nucleatum prior to P. gingivalis interfered with the opsonophagocytosis function of sera against P. gingivalis. In adoptive T-cell transfer experiments, in vivo protective capacity of type 2 helper T-cell clones (Th2) from group 2 was significantly lower than type 1 helper T-cell clones (Th1) from group 3 against the lethal dose infection of P. gingivalis. Western blot analysis indicated a different pattern of recognition of P. gingivalis fimbrial proteins between sera from group 2 and group 3. In conclusion, these studies suggest that exposure of a host to F. nucleatum prior to the periodontal pathogen P. gingivalis modulates the host immune responses to P. gingivalis at the humoral, cellular and molecular levels.

Genetic control of susceptibility to Porphyromonas gingivalis-induced alveolar bone loss in mice

Periodontal disease affects a large percentage of the human population. Resorption of the alveolar bone of the jaw is a pivotal sequela of periodontal disease, because this bone is the attachment site for the periodontal ligaments that anchor the teeth. Using a murine model in which alveolar bone loss is induced by oral infection with Porphyromonas gingivalis, a gram-negative bacterium associated with human adult periodontal disease, we provide evidence suggesting that susceptibility to such bone loss is a genetically determined trait. AKR/J, DBA/2J, and BALB/cByJ or BALB/cJ mice were highly susceptible, while A/J, A/HeJ, 129/J, SJL/J, and C57BL/6J mice were much more resistant. When susceptible BALB/cJ and BALB/cByJ mice were crossed to resistant strains, two patterns were observed. (BALBc/ByJ x C57BL/6J)F(1) offspring were susceptible, suggesting C57BL/6J has recessive resistance alleles, while (BALB/cJ x A/J)F(1) mice were all resistant, suggesting that A/J mice have dominant resistance alleles. These results suggest a tractable genetic basis for P. gingivalis-induced alveolar bone loss and open the possibility of exploiting the mouse model to identify loci important for host susceptibility and resistance to periodontal disease.

The role of immune responses in bone loss during periodontal disease

A network of cytokines and other soluble mediators unites the immune system and bone; bacterial infections induce immune responses which may perturb this network. Periodontal diseases are Gram-negative infections resulting in bone loss in the jaw. Evidence is presented that immune responses to these infections produces net resorption of bone.

Adhesion molecule deficiencies increase Porphyromonas gingivalis-induced alveolar bone loss in mice

Alveolar bone resorption can be induced in specific-pathogen-free mice by oral infection with Porphyromonas gingivalis (P. J. Baker, R. T. Evans, and D. C. Roopenian, Arch. Oral Biol. 39:1035-1040, 1994). Here we used a mouse strain, C57BL/6J, which is relatively resistant to P. gingivalis-induced bone loss to examine whether partial or complete deletion of various adhesion molecules would increase susceptibility. Complete deletion of P-selectin or nearly complete lack of expression of intercellular adhesion molecule 1 (ICAM-1) led to increased susceptibility to bone resorption after oral infection, while a hypomorphic defect in beta(2)-integrins did not. Both the total amount of bone lost and the number of sites at which there was significant loss were increased in mice deficient in either ICAM-1 or P-selectin. Each of the three adhesion molecule deficiencies was sufficient to decrease P. gingivalis-specific serum immunoglobulin G responses, but lower antibody titers did not lead to increased bone loss in partially beta(2)-integrin-deficient mice. In conclusion, P-selectin and ICAM-1 deficiencies increase susceptibility to and severity of alveolar bone loss after P. gingivalis infection. This finding underscores the importance of innate immunity in protection against P. gingivalis-induced alveolar bone resorption.

Heterogeneity of Porphyromonas gingivalis strains in the induction of alveolar bone loss in mice

These experiments examine alveolar bone loss in a model in which specific pathogen-free mice are exposed orally with Porphyromonas gingivalis. Alveolar bone loss was induced as a result of a specific infection with P. gingivalis, rather than other environmental antigens. Infection with live P. gingivalis was required, as significant bone loss did not follow gavage with formalin-killed P. gingivalis. The virulence of different strains of P. gingivalis was compared. Two laboratory strains of the bacteria (ATCC 53977 and W50) and a mutant strain lacking the 43-kDa fimbrillin (strain DPG3) induced bone loss. P. gingivalis 381, however, did not induce bone loss. There was a strong immunoglobulin G (IgG) antibody response to infection with each strain but a significant serum IgA response only to strain 381. These studies show that in mice with a background oral microflora bone loss is induced by a specific infection with P. gingivalis and that bacterial strain variation is important in determining whether alveolar bone loss will ensue.